The invention relates to a tidal power plant and a method for the creation thereof.
The tidal power plants as discussed herein are driven by a watercourse or a flow of air or a tidal flow. Wind power plants and tidal power plants arranged in a conceptually respective manner are known. A typical configuration provides a propeller-like turbine which revolves with a horizontal rotational axis on a machine nacelle in which an electric generator is disposed which is driven by the turbine shaft. The machine nacelle is erected on a tower above a foundation structure. Vertical-axis rotors such as Darrieus rotors represent modifications for example. Furthermore, turbines can be housed in a jacket housing with the effect of a Venturi nozzle especially for utilizing slow tidal flows and can be mounted via a radially outer support frame. Such installations represent variants of generic tidal power plants which are considered in the present application.
The erection of large-size wind or tidal power plants is a challenge especially for an offshore location with a sunk foundation structure. One of the difficulties relates to the centering of the foundation structure in order to place a machine nacelle on a coupling apparatus on the foundation structure in such a way as described in EP 1 366 287 B1 that the rotational axis of the turbine lies in a predetermined operating area. If foundations for forming the foundation structure are cast on site, centering can not always be ensured with the required precision. This is all the more true when concrete elements prefabricated in dry docks are sunk for forming the foundation structure at the place of installation. Even in the case of a careful preparation of the seabed there is often the necessity for correcting the centering.
A pile-like structure which is mostly a steel tube is rammed into the ground at first at the installation location for a monopile foundation. A centering error will usually occur in this process, so that an external tube of a larger diameter is placed and aligned on the same for vertical orientation. The intermediate space between the rammed pile and the external tube will be filled with cement in order to produce a so-called grout connection. The disadvantageous aspect of this foundation variant is the high amount of installation work. Furthermore, several monopiles are usually necessary for large-size tidal power plants, on which a supporting platform will then be erected.
An inexpensive alternative for the formation of a foundation structure is provided by gravity foundations made of concrete. They can be prefabricated at the dock in their entirety or as partial components and can be dragged as floating units to the place of installation and can be sunk there. Corrective elements are proposed for the correction of an angular position of such a foundation structure by DE 10 2008 000 382 A1, which corrective elements respectively consist of a paired sequence of cylindrical elements with obliquely beveled contact surfaces. By twisting two successively following elements, there will be a bend in the stack sequence which allows centering the longitudinal axis of the stack in relation to the perpendicular. The disadvantageous aspect in this approach is that it is necessary to perform the relative positioning of the corrective bodies at the installation location on the ground of the sea. Furthermore, their position needs to be fixed in a secure manner, which proves to be difficult as a result of the obliquely disposed contact areas and the resulting elliptical borderings of the corrective bodies.
The setting down of a foundation structure on the seabed for a tidal power plant is further described in WO 2007/083105 A1, with draw works being provided on the foundation for centric orientation. Such an approach increases the complexity of installation however. Furthermore, concentrated loads will be generated in the region of the draw works on the foundation, for which the foundation structure needs to be configured. It is a further problem that over time the support points of the foundation will yield in the region of the draw works as a result of erosive processes, thus leading to changes in the position and orientation of the foundation structure. A further variant for centering a bottom tower part on a tripod disposed obliquely on the seabed for forming a tidal power plant is described by WO 2004/015207 A1. It is disadvantageous that the corrective steps need to be performed on-site and dangerous diving work is necessary.